Prior to the present invention, as shown for example by Williams et al, U.S. Pat. No. 4,257,953, assigned to the same assignee as the present invention, aromatic bis-etherphthalimides were prepared by reacting bisphenoxide salts with nitro-substituted N-organophthalimides, for example, 4-nitro-N-methylphthalimide, or a mixture thereof with 3-nitro-N-methylphthalimide. These nitro-substituted N-organophthalimides can be made by the process as shown by Cook et al, U.S. Pat. No. 4,005,102, assigned to the same assignee as the present invention.
In Cook et al, the nitration of N-organophthalimides is achieved by refluxing a mixture of the N-organophthalimide, concentrated nitric acid, concentrated sulfuric acid and methylene chloride to produce the corresponding nitro-substituted N-organophthalimide. The desired nitrophthalimide is then initially isolated from the nitration mixture as the organic methylene chloride phase. The methylene chloride phase is then combined with the methylene chloride extract of the acid phase and the total passed through a column of silica gel to remove traces of sulfuric acid. The nitrophthalimide was then recovered by evaporation of the methylene chloride.
The aromatic bis-etherphthalimide was then made in accordance with the above Williams et al patent, which utilizes the nitrophthalimide in a heterogeneous mixture of the alkali metal bisphenoxide salt, nonpolar organic solvent and phase transfer catalyst. Although the aforementioned procedure involving the isolation of the nitrophthalimide from the nitration reaction mixture prior to its reaction with the bisphenoxide salt achieves valuable results, it nevertheless requires the time consuming step of isolating and handling the nitrophthalimide prior to its contact with the alkali metal bisphenoxide salt.
The present invention is based on the discovery that aromatic bis-etherphthalimides can be made without the isolation of the nitro-substituted N-organophthalimide from a polychlorinated C.sub.(1-3) alkane solution obtained from the nitration reaction mixture, by directly utilizing the polychlorinated C.sub.(1-3) alkane phase of the nitration reaction mixture consisting of a solution of the nitrophthalimide in the polychlorinated C.sub.(1-3) alkane with a mixture of alkali metal bisphenoxide salt and nonpolar solvent. Preferably, the addition of the polychlorinated C.sub.(1-3) alkane solution of the nitro-substituted N-organophthalimide to the alkali metal bisphenoxide salt is achieved while the bisphenoxide salt is in contact with the nonpolar organic solvent while it is refluxing. After the polychlorinated C.sub.(1-3) alkane has completely distilled from the resulting reaction mixture, the phase transfer catalyst can be added. Otherwise, undesirable side-reaction can occur resulting in undesirable polychlorinated C.sub.(1-3) alkane polymeric reaction products.